Preliminary report on the water resources of northeast Maui

Takasaki, Kiyoshi; Yamanaga, George

Northeast Maui, as described in this report, includes about 165 square miles of the northeast and east slopes of Haleakala. Large forest reserves, on lands too wet for cultivation or at altitudes too high for development, make up much of the area. The lower drier slopes are used mainly for grazing, with smaller areas in orchards and taro cultivation, Population in 1969 was less than 1,500. Average rainfall is about 180 inches per year, which is equivalent to 1,420 mgd (million gallons per day). Although water use in the area is small, less than 5 mgd, the area is an important watershed and source of water for sugar cane irrigation in central Maui and for domestic use on the upper southwest slopes of Haleakala. An average of about 160 mgd of water is exported for sugar cane irrigation through an extensive system of ditches and tunnels. The principal ditches take all the dry-period water from Makapipi to Honopou Streams at about an altitude ranging from 1,200 to 1,000 feet. About 2 mgd of domestic water is diverted from streams through a collection system running from Waikamoi to Honomanu Stream at an altitude of 4,000 feet and from Waikamoi to Puohokamoa Stream at an altitude of 3,000 feet. The occurrence of water is largely controlled by the ability of the surface rocks to absorb the abundant rainfall. Where the surface is comprised of highly permeable lava flows and cinders of- the Hana Volcanic Series, the youngest rocks in the area, much of the rain enters the ground as recharge to ground-water bodies and overland stream runoff is low and streams are mostly intermittent. Where the surface is comprised of less permeable and older lava flows of the Kula Volcanic Series, much of the rain is dispersed as overland stream runoff or is quickly returned to the surface from shallow and small around-water bodies, and streams are mostly perennial. Most streams are perennial between altitudes 1,000 and 2,000 feet. Streamflow above these altitudes depends mostly on intensity and persistency of rainfall. Development of stream supplies is best in areas where lava flows of the Kula Volcanic Series crop out. Ground water occurs in perched bodies in Hana and Kula rocks, as artesian perched bodies in the upper transitional part of the Honomanu Volcanic Series, and as basal water in the Hana and Honomanu Volcanic Series near the shore. Other probable occurrences of ground water, not yet identified or tapped by wells and tunnels, include dike-impounded water bodies in Honomanu rocks and inland basal-water bodies in Kula and Honomanu rocks. The chemical quality of the water is generally excellent in northeast Maui.